Process for sealing a surface and resultant surface

ABSTRACT

A PROCESS FOR SEALING CONCRETE BY PROVIDING A COMPOSITE OF TWO LAYERS, ONE LAYER BEING CAPABLE OF BRIDGING CRACKS IN THE CEMENT EVEN DURING EXTREME TEMPERATURE VARIATIONS AND THE OTHER LAYER BEING TOUGH AND ABRASIONAND WEAR-RESISTANT, BOTH LAYERS COMPRISING A URETHANE POLYMER RESULTING FROM IN SITU CURING OF EVENLY APPLIED, SEPARATE COATINGS OF MOISTURE CURABLE, ISOCYANATE TERMINATED PREPOLYMER.

March 27, 1973 G- SCHUMACHER 3,223,163

PROCESS FOR SEALING A SURFACE AND RESULTANT SURFACE Filed May 28, 1971Tea L.

AT TORNE Y5 United States Patent 3,723,163 PROCESS FOR SEALING A SURFACEAND RESULTANT SURFACE Gerald F. Schumacher, St. Paul, Minn., assignor toMinnefita Mining and Manufacturing Company, St. Paul,

inn.

Continuation-in-part of abandoned application Ser. No. 814,754, Apr. 9,1969. This application May 28, 1971, Ser. No. 147,875

Int. Cl. B32b 13/12; B44d 1/14 US. Cl. 117-72 Claims ABSTRACT OF THEDISCLOSURE A process for sealing concrete by providing a composite oftwo layers, one layer being capable of bridging cracks in the cementeven during extreme temperature variations, and the other layer beingtough and abrasionand wear-resistant, both layers comprising a urethanepolymer resulting from in situ curing of evenly applied, separatecoatings of moisture curable, isocyanate terminated prepolymer.

This application is a continuation-in-part of copending application Ser.No. 814,754, filed Apr. 9, 1969, now abandoned.

This invention relates to a process for sealing concrete; moreparticularly, it relates to a process for sealing concrete by means ofcertain polyurethane compositions.

Concrete structures are subject to cracking and other forms ofdegradation. The problem is particularly pronounced where the concreteis exposed to wide variations in temperature and other weatherconditions. The cracks provide passages for water and other fluids whichalone or because of dissolved chemicals can prove deleterious to theconcrete and reinforcing members, as well as to objects situated belowthe concrete on which the fluids drip. Especially troublesome is thedripping of water containing corrosive salts through concrete parkingdecks or ramps onto automobiles below.

Current methods of sealing concrete slabs against fluid penetrationthrough concrete stress cracks utilize various polymeric materials.There is a general consensus among people versed in sealing concretethat all such commercially available systems fail to do an adequate jobof stopping moisture and other fluid penetration through concrete stresscracks. These coatings fail for a variety of reasons, especially due toeither lack of adhesion and/or their inability to elongate over existingor newly formed cracks in the slab. These cracks change their dimensionwhen exposed to a wide temperature range causing tearing of the appliedcoating. Until now it was thought to be essential to sacrificeelasticity for toughness in order to provide a wearable surface.

Although there are several prior art techniques relating to sealingindividual cracks in concrete surfaces by pouring a curable compositioninto the crack, such techniques are undesirable for several resasons.For example, the Sealing of individual cracks provides no protectionagainst leakage through newly formed cracks. Furthermore, leakage mayoccur through cracks which are not easily located or detected. Moreover,even if all newly formed cracks can be easily located, this piecemealsealing of cracks is likely to continue over a period of years as newcracks continue to come into existence. The irregular patchworkresulting from the sealing of individual cracks is also aestheticallyundesirable. Consequently, piecemeal sealing of individual cracks isquite inefficient and;highly undesirable.

It has been found that prior art urethane compositions which reportedlyare useful for the sealing of individual cracks do not provideacceptable sealant coatings within the meaning of the present inventionbecause a continuous sealant coating must meet very stringentrequirements. For example, the sealant coating must be easily applied ina thin film, and the coating must be tough and abrasionandwear-resistant.

It is an object of this invention to provide a method for sealingconcrete stress cracks to prevent leakage of deleterious materialstherethrough.

Another object is a method which provides a durable, wear-resistantcomposite coating for sealing concrete stress cracks against leakage.

Another object is the provision of such a method which is economical andeasy to perform by unskilled labor.

Another object is to provide a means for the sealing of a concretesurface to prevent leakage of materials therethrough even though newcracks may subsequently come into existence.

These and other objects are accomplished by the present invention whichin general comprises applying a thin base layer comprising at least onecoating comprising a moisture curable, NCQ terminated prepolymer,wherein Q is oxygen or sulfur, to concrete or other surface, andallowing said prepolymer to cure in the presence of moisture to providecured, resilient, elastomeric, crosslinked polyurethane orpolythiourethane. A thin overlayer of polyurethane or polythiourethanewhich is hard, tough, traffic-durable, flexible, resilient, andwear-resistant is then applied over the base layer, the overlayer beingtougher and more wear-resistant than the base layer. The overlayer alsoexhibits higher tensile strength than the base layer.

In addition to conventional fillers and the like which may also bepresent, the cured polymer matrix for each layer may contain thoroughlydispersed therethrough up to about based on the weight of said curedpolymer, of an organic resin which is compatible with the polymer (i.e.,will not separate and destroy the homogeniety of the matrix and will notreact with or interfere with the curing mechanism). Preferred examplesof such a resin include a low molecular weight polystyrene, coumaroneindene, coal tar, or chlorinated polyphenyl resins.

The coating compositions which are useful for the base layer and theoverlayer are one-part, generally solventcontaining systems which arecapable of storage in a hermetically sealed container at 25 C. for atleast 6 months. Preferred are prepolymers from a polyisocyanate and apolyol having a functionality greater than 2.

While it is preferred to include conventional fillers in the base layerand the overlayer, there are applications where fillers are not requiredin either of the layers, e.g., where it is desired to seal a surfacewith a transparent coating.

Moisture curable prepolymers from a polyether or polyester polyol and anequivalent excess of a polyisocyanate in combination with variousfillers represent the preferred coating compositions for practicing thisinvention, the prepolymer simply being applied from a container with atrowel or other suitable means and cured in place by water generally inthe form of atmospheric moisture. Two part formulations in which anisocyanate is cured with an organic hydroxy compound or the like notonly require on site mixing but also are subject to bubble formation orpossibly incomplete curing due to the preference of the NCO-waterreaction versus the NCO-organic hydroxy] reaction. Since concrete isknown to have an aflinity for water, this competing reaction is serious.

In general, the NCQ prepolymers are the reaction prod net of anequivalent excess of at least one organic polyisocyanate orpolythioisocyanate with one or more organic compounds having a pluralityof hydroxy, thiol, or amine groups, the molar excess (molar ratiogreater than one) being needed to obtain the isocyanate orthioisocyanate termination. The prepolymers generally have an averagemolecular weight ranging from about 500 to about 10,000, and preferablyfrom 800 to 7,000.

Any of a wide variety of organic polyisocyanates may be employed in thereaction, including aromatic, aliphatic and cycloaliphatic diisocyanatesand combinations of these types. The aromatic diisocyanates include2,4-toluene diisocyanate, mixtures thereof with 2,6-toluene diisocyanate(usually about 80/20 by weight, respectively), methylenebis(4-phenylisocyanate), m-phenylene diisocyanate,3,3'-dimethyl-4,4-diphenylene diisocyanate, 3,3-dimethoxy-4,4'-bisphenylene diisocyanate, 3,3-diphenyl- 4,4-biphenylenediisocyanate, 4,4'-biphenylene diisocyanate, 4chloro-1,3-phenylenediisocyanate, 3,3'-dichloro- 4,4'-biphenylene diisocyanate, and1,5-naphthalene diisocyanate. Arylene diisocyanates, i.e., those inwhich two isocyanate groups are attached directly to an aromatic ring,are preferred. The diisocyanates may contain other substitutents,although those which are free from reactive groups other than the twoisocyanate groups are ordinarily preferred. In the case of the aromaticcompounds, the isocyanate groups may be attached either to the same orto dilferent rings. The preferred polyisocyanates are either thecommercially available mixture of toluene diisocyanates which contains80% 2,4-toluene diisocyanate and 20% 2,6-toluene diisocyanate or 4,4'-methylene bis-(phenylisocyanate). Commercially available polymericaromatic isocyanates having an NCO functionality greater than 2.0 arealso quite useful.

Aliphatic compounds such as ethylene diisocyanate, ethylidenediisocyanate, propylene-1,2-diisocyanate, butylene-1,3-diisocyanate,tetramethylene diisocyanate, hexamethylene diisocyanate anddecamethylene diisocyanate are suitable as are alicyclic compounds suchas 1,2- and 1,4-cyclohexylene diisocyanates and 4,4'-methylene-bis-(cyclohexylisocyanate). Suitable isothiocyanates include hexamethylenediisothiocyanate, m-phenylene diisothiocyanate, m-tolylenediisothiocyanate, and 2,4-toluene diisothiocyanate.

The organic compounds which react with the polyisocyanates andpolyisothiocyanates to obtain the NCQ terminated prepolymers arepreferably hydroxy, thiol, and amine (primary or secondary) terminatedpolymers having a molecular weight preferably on the order of 400 ormore. Typical polymer backbones include polyethers, polyepihalohydrins,polythioethers, polysulfides, polyesters both of the condensation andlactone type, and polyhydrocarbons.

Illustrative polyethers are the following: poly(oxyethylene) glycols,poly(oxypropylene) glycols, poly(oxypropylene)-poly(oxyethylene)copolymers, poly(oxytetramethylene) glycols, poly(oxybutylene) glycols,the tetrafunctional ethylene oxide-propylene oxide block copolymersinitiated with ethylene diamine, and poly(oxypropylene triols initiatedwith low molecular Weight triols such as trimethylolpropane, glycerol,and 1,2,6-hexanetriol.

Thiol terminated poly(oxyalkylene) glycols usually prepared by theacid-actalyzed condensation of thiodiethylene-glycol with itself (i.e.,homopolymers of thiodiethyleneglycol) or at elevated temperatures withformaldehyde, paraformaldehyde, etc., or polyols such as 1,4-butanediol, may be employed in the preparation of NCQ terminatedprepolymers. Polymers of this type with molecular weights of at least750 are described in U.S. Pat. No. 2,900,368.

Hydroxy-terminated polysulfides such as are disclosed in U.S. Pat. No.3,168,119, may also be employed in the practice of this invention.

Other suitable polysulfides are the liquid mercapto terminatedpolysulfides such as are disclosed in Patrick et al., U.S. Pat. No.2,466,963, exemplary of which are those available from the ThiokolCorp., under the trade names LP-2 and LP-3.

Exemplary hydroxy terminated polyesters are polyethylenepropyleneadipate, polyethylene adipate, polyethylene adipate (70)-phthalate (30),and polyneopentyl sebacate. In general, the most suitable polyesters arechiefly linear in type with melting point levels of C. or lower. Themolecular weight may range between 200 and 10,000 and preferably between1,000 and 3,000.

Hydroxy terminated lactone polyesters such as are described in U.S.Pats. Nos. 3,169,945 and 3,186,971, are also effective in preparing NCQterminated prepolymers as are hydroxyl terminated polymers from vinylmonomers such as are disclosed in U.S. Pats. Nos. 2,792,382 and3,055,942.

While not essential, a catalyst may be employed in the preparation ofthe prepolymer. Suitable catalysts include tertiary amines, such asdimethylcyclohexyl amines, triethylamine, 1,2,4-trimethylpiperazine orheavy metal compounds soluble in the reaction system such asiron-acetoacetate and dibutyltin dilaurate.

The prepolymer reaction conditions and the reaction time vary dependingon the kind and molecular weight of the polymer reactants, the kind andthe amount of the diisocyanate to be used, and the type of catalystemployed, if any. Generally, a temperature between 50 C. and C. and areaction time between 5 and 300 minutes is employed.

Catalysts, if employed, are generally present to the extent of about0.01 to about 1.0% by weight of the total weight of the reactants. Formoisture curable prepolymers, 1,2,4-trimethylpiperazine and dibutyltindilaurate represent the preferred catalysts.

The presence of crosslinks in the cured urethane type polymer isessential to provide the desired physical properties. Crosslinks areintroduced in the conventional manner by the presence in the curablesystem of a branched or polyfunctional material such as triortetra-functional hydroxy, thiol, amine, isocyanate or thioisocyanatecompound. Triols, such as polypropylene oxide triols, are the preferredcrosslinking agents. The molecular weight per crosslink, Me, has beendefined as the unit weight of polymer divided by the number of crosslinkjunctions or branch points in the unit weight of polymer. (Saunders andFrisch, Polyurethanes, Part I, p. 266.) The Me for the cured polymers ofthe composition of this invention should be between about 500-50,000 andpreferably between 1500 and 10,000. One may vary the tensile strength,elongation and toughness of the polyurethane coatings according to themethods described in The Relationship Between Polymer Structure andProperties in Urethanes, Rubber Chemistry and Technology, vol. 33, No.5, p. 1259 (December 1960).

Moisture curable, crosslinkable NCQ terminated prepolymers optionallycontaining polystyrene resin may be marketed in a single container andapplied directly to the concrete or, more preferably, to concrete whichhas been primed with an adhesion promoter.

In commercial applications (e.g., when coating trafiic surfaces ingarages) many secondary surfaces (arcawise) are encountered, such asrubber or metal fiashings, coves, pipes, electrical conduits, lightstandards, railings, expansion butt plates, etc. To insure properadhesion between the composite coating and such secondary surfaces, itis desirable to initially prime such surfaces with appropriate primerssuch as two-part wash primers, epoxies, various silane-containingprimers, phenolics or other common adhesion promoting agents.

The moisture curable coatings of this invention are applied directly tothe substrate by pouring from the container and spreading the coatingusing a sawtooth notched rubber squeegee, a paint roller, a standardpush broom, or brushes. The notched squeegee application is preferredfor applying pourable (500-4000 cps. viscosity) coatings because it isquite easy to obtain the desired dry film thickness by varying the sizeof the sawtoothed notches. Spray application techniques can also beused.

Heavier bodied coatings (5000l00,000 cps.) are ap plied by hand trowel,spray or paint roller with greater skill required to obtain the desiredfilm thickness.

The base layer can be applied in a single coat or in two or more coatsto obtain the desired film thickness of generally from -60 mils.Preferably, the base layer is in the range of about 20 to about 60 milsthick.

The overlayer is preferably in the range of 10 to about 40 mils inthickness, although overlayers of 2 to 10 mils are useful for aestheticor color matching purposes. When this overlayer is to be greater than 20mils in thickness, it is preferable to sequentially apply two thin coatswhich together provide the desired thickness.

For light to, moderate trafiic areas (pedestrian, automobile parking,driving aisles, etc.) the composite coating is generally about 40 milsin thickness (about 20 mils base layer and about 20 mils overlayer), andfor heavy traflic areas the thickness is about 60 mils (about 20 milsbase coating and about 40 mils overlayer).

An indication of the ability to maintain a seal over cracked or crackingconcrete can be measured for any particular system by a test,(hereinafter referred to as crack extension test) the details of whichare as follows:

A one inch x 2% inch X 40-80 mils thick wet film of the polyurethanecoating is cast across the ends of two 3 inch x 2 inch x 1 inch primedconcrete blocks which are separated with a small (2 inch x 1 /2 inch xinch) concrete block. The small block is centered on, and firmly bondedto, one side of one of the larger concrete blocks, the top surface ofthe small block being flush with the top surfaces of the larger blocks,and the blocks are arranged such that the sample bridges a hairlinecrack at the joint of the small block and one of the larger blocks.Priming is done with a 5% by weight aqueous solution ofgamma-aminopropyltriethoxy silane. Following a cure at 75 'F./50% RH fora minimum of one week, a 30-60 mil dry film is obtained. Using a tensilemachine described in Federal Specification 'ITS00230, the larger blocksare separated at a rate of /s inch per hour until the hairline joint isopened to inch, and the coating is continually examined for failure inthe form of cracking while the blocks are being separated.

Experience has shown that compositions which pass the above test bysuccessfully bridging this 7 inch gap TABLE I Property Minimum PreferredPercent elongation 200 1 300 Crack extension, inch.g 2 %i 1 The greaterthe elongation the more desirable the base layer. 1 Without failure.

Other desirable properties are shown in Table 11.

TABLE II Property Minimum Preferred Tensile strength, p.s.i 60 200-1,000 Rex Hardness 20 3545 Adhesion, peel, lbs/in. width 5 -20 Thefollowing represent minimum and preferred properties, measured at 75 F.,for polyurethane overlayers which are suitable in the practice of theinvention:

TABLE III Property Minimum Preferred Percent elongation- 25 150 Tearstrength, lbs./in 125 300-450 Tensile strength, p.s i 800 1, 200 RexHardness -95 Abrasion resistance (H 2 wh at 1000 gra 1,000 cycles),grams 1 0.75 1 0.2 Adhesion to base coat, peel 1 Maximum weight loss. 15 lbs/in. width or cohesive failure of base coating.

All data reported herein is taken from degassed coating samples. Thedegassing procedure as well as the other testing procedures are asfollows:

Degassing The sample is placed in a container and a vacuum drawn ofabout 5 mm. Hg or less for about 3 0 minutes. Heavy-bodied coatings mustbe diluted with heptane to a pourable consistency before degassing.

Casting the film Following degassing, the film to be tested should becast immediately in an open aluminum mold, typical measurements being 8inches wide, 8 inches long, and 20 to 80 mils deep, taking precautionsnot to introduce air into the sample.

Curing the coating Place the filled mold on a level surface at 77 F. and50% relative humidity. After two days at these conditions, remove thecoating from the mold; invert the film; and continue the cure for fiveadditional days at the same conditions. A cured film measuring about 15to 60 mils thick should result.

Preparation of dumbbells Tensile strength and elongation Pull thedumbbells to failure on a tensile testing machine having a sensitivityof pound, and a jaw separation rate of 2 inches per minute. Record themaximum force and distance between the bench marks just before eachspecimen fails and calculate tensile strength and elongation in theconventional manner.

Other tests (a) Moisture vapor transmission-according to ASTM E96-53,Method B;

(b) Tear strength determined by ASTMD-624-54;

(c) Adhesion-Canvas to concrete (concrete primed with 5% by weightgamma-aminopropyltriethoxy silane in water), according to Fed. Test Std.601-8031 except pull used; and

(d) Abrasion resistance according to ASTM-D-l044 employing an H22 wheelat 1000 grams-1000 cycles.

In order to promote a better understanding of the present invention, thefollowing non-limiting examples are given wherein all parts andpercentages are by weight unless otherwise stated.

EXAMPLE 1 A prepolymer useful for providing a base layer is preparedfrom the following composition:

Ingredient Equivalents Parts/weight 2,000 MW. dlcl (polypropyleneoxlde).-.. 0.3 300.6 4,000 MW. triol (polypropylene rxide) 0.6 780Toluene". 134 Toluene dnsocyannte (BO/20 mixture by weight of 2,4 and2,6 isomers) 1.8 156 Dibutyltin dllnurate 1.0

To a nitrogen purged resin flask is added the diol, triol and toluene.Toluene diisocyanate is added with mixing and the temperature is raisedto 80 C. and held at the temperature for 4 hours, then cooled to 60 C.and the dibutyltin dilaurate catalyst added. At this point theprepolymer has a Gardner-Holdt viscosity of 17-27 stokes and a NCOequivalent weight of 1400-1800.

The prepolymer is then combined in the order shown in Table IV with thefollowing ingredients in a one quart Baker-Perkins mixer over which ismaintained a dry nitrogen blanket.

TABLE IV Ingredients: Parts by weight (1) Titanium dioxide 38.6 (2) Zincoxide 38.6 (3) Carbon black 0.85 (4) Talc 300 (5) Pyrogenic silica 48(6) Styrene resin/toluene (56.6% by weight styrene resin) 530 (7)Prepolymer 500 (8) Toluene -150 (9) Dibutyltin dilaurate 8 EXAMPLE 2Another useful base layer composition is prepared with the followingingredients:

TABLE VI Parts by weight Titanium dioxide 96.5

Zinc oxide 96.5

Carbon black 2.12

Talc 750.0

Pyrogenic silica 117.4 Prepolyrner of Example 1 2085.0 Toluene 878.0Dibutyltin dilaurate 12.6

After a 7 day cure at 75 F./ RH the above compositon is tested with thefollowing results obtained at 75 F.:

TABLE VII Tensile strength 900 p.s.i.

Elongation 440% Moisture vapor transmission rate grams/sq. meter/day,

8.0 perms.

Adhesion 22 lbs/in. width.

Tear strength 120lbs./in.

Abrasion resistance 1.0 g. wt. loss.

Crack extension test 75.

Rex hardness in. without failure.

Application characteristics Suitable for trowel,

spray, or squeegee.

EXAMPLES 3-5 Other useful prepolyrners for the base layer are pre- 5.0pared from the reactants of Table VIII below.

TABLE VIII Molecular Weight No. of equivalents of- 150- Equivalentscyanate 1 isocy- Example Diol Trlol Dlol Triol type anate Mo "2,6000.500 0.750 TDI 2.50 4, 372 134 2.00 1.35 'IDI 5.80 5, 704 4, 000 0.3000.600 MD]! 1.80 6, 323

n Polytetramethylene oxide type.

b Poly-e-caprylactone type.

c Polypropylene oxide type.

d 'Irlmethylolpropane.

a 80/20 a l-toluene ditsocyanate/2,6-toluene dhsooyanate. l Methylenebis (4-phenyl1socyanate).

Prior to mixing with the prepolymer, ingredients (1)- (5) are dried at350 F. to a moisture content of less than 0.05%.

The composition is then tested with the following results, obtained at75 F.:

TABLE V Tensile strength (ASTM D412- 64T) Elongation (ASTM D412- 64T)Rex hardness 879 p.s.i.

spray, or squeegee. Adhesion to concrete surface (ASTM D903-49) 20lbs/in. width. Tear strength (ASTM D624- 54 (Die C)) 206 lbs./in.

Abrasion resistance 1.5 g. wt. loss.

The surface to which the base layer is applied should be dry and clean(i.e., free from surface contaminants such as dust, dirt, oil, etc.).Sandblasting or acid etching (e.g., with muriatic acid) of the concretesurface is preferred. Priming of the concrete surface is also highlypreferred.

The overlayer is applied over the base layer after the base layer iscured to a firm, tack-free state. The overlayer is applied according tothe same techniques as are used for the application of the base layer(i.e., sawtooth notched squeegee, paint roller, push broom, sprayequipment or brush). The purpose of the overlayer is to provide a hard,tough, trafiic-durable, abrasionand wear-resistant surface.Consequently, the NCQ terminated prepolyrners used for the overlayermust be capable of moisture-curing to a crosslinked, resilient layerwhich is harder than the base layer and which is tougher and morewear-resistant than the base layer. The overlayer also exhibits highertensile strength than the base layer.

EXAMPLE 6 A prepolymer useful for the overlayer is prepared from thefollowing ingredients usingthe same procedure as described above inExample 1:

Ingredient Equivalents Parts/weight 1,000 MW. polypropylene glycol dlol2.0 1, 000 750 MW. polypropylene glycol trlol 1. 250 Toluene -175Toluene dlisocyanate (80/20 mixture by weight of 2,4 and 2,6 isomers) 6.0 522 Dibutyltln riilmrmhz 0.

The Gardner Holdt viscosity of this composition is 15-25 stokes and theNCO equivalent weight is 600-750.

The prepolymer is then combined in the order shown in Table IX with thefollowing ingredients in a one quart Baker-Perkins mixer over which ismaintained a dry nitrogen blanket.

TA'BLE IX Ingredients: Parts by weight (1) Titanium dioxide 25.0 (2)Zinc oxide 25.0 (3) Carbon black 0.5 (4) Talc 350 (5) Antioxidant 1 5.0(6) U.V. Absorber 5.0 (7) Prepolymer 500 TABLE X Tensile strength 2620psi. Elongation 170%. Rex hardness 75 F. 90. Adhesion (ASTM D903-49,primed concrete) 20 lbs/in. width. Tear strength (ASTM D624-54,

Die C) 378 lbs/in. Abrasion resistance 0.2 g. wt. loss.

It has been found that curable compositions which are useful for theoverlayer are not suitable as base layers because they do not providecoatings which will bridge cracks under all variations of temperatureand environment without cracking. However, when applied to the surfaceof the base layer, the overlayer does not crack nor does it inhibit theability of the base layer to bridge cracks successfully. This result wastotally unexpected in view of the relatively poor elongation propertiesof the overlayer.

While the primary utility of the process of this invention relates tocoating concrete surfaces, it is to be understood that the process ofthis invention is particularly suitable for providing a continuouscoating for sealing cracks in any type of substrate wherein leakagetherethrough would be a problem. The coating may be applied eitherdirectly to the concrete, wood, or other substrates such as metal,ceramic tile, terrazo, quarry tile, marble, stone aggregate, foamedinsulating surfaces, or indirectly, as to an intermediate coating suchas asphalt which had been applied to such substrate. The process of theinvention may also be used to protect any surface from wear ordegradation due to the elements, e.g., driveways, parking areas,walkways, sidewalks, artificially-surfaced water ponds or pools,promenades, roofs, balconies, etc.

To aid in preventing skidding on the coating surface, conventionalanti-skid agents may be added to the composition which is used for theoverlayer. For example, finely divided walnut shells, quartz, sand,silicon carbide,

aluminum oxide, or other anti-skid materials can be used. It is oftenpreferable to prime the surface of some antiskid agents before blendingthem into the composition, e. g., conventional amino silanes are veryuseful as primers for quartz, sand, silicon carbide and aluminum oxide.The amount of anti-skid agent normally used is about one part by volumefor each five parts by volume of coating composition.

For fire-proofing applications, one may include various fire retardantfillers in the coating compositions. For example, useful fire retardantmaterials such as chlorinated paraffin's, antimony oxide, borates orphosphates can be used.

For decorative applications colored quartz granules (typically 11 to 28mesh) can be applied to a very thin (e.g., 10 mils) wet, uncuredoverlayer using broadcast distribution methods. After this thinoverlayer has cured, all lose quartz granules are removed and a clear,colorless acrylic or urethane seal coat is applied to protect thecolored quartz granules from wear. This decorative system is only usefulin non-traffic or light pedestrian trafiic areas.

What is claimed is:

1. A process for sealing a surface to prevent leakage through crackstherein in a manner such that the sealed surface is alsotraffic-durable, the process comprising:

(a) applying to said surface a base layer comprising at least onecoating comprising a moisture curable, crosslinkable NCQ terminatedprepolymer, wherein Q is oxygen or sulfur, wherein said prepolymer, uponcuring in the presence of moisture, provides a resilient, elastomeric,crosslinked polymer coating capable of sealing said surface,

(b) curing said crosslinkable NCQ terminated prepolymer to provide acrosslinked polymer coating which exhibits an elongation of at least200%, a tensile strength of at least 50 psi, a peel adhesion of at least5 lbs/in. width, and a crack extension characteristic of at least inchat room temperature,

(0) applying to said cured base layer a flexible, traflicdurable,abrasion-resistant overlayer comprising at least one coating comprisinga moisture-curable, crosslinkable, NCQ terminated prepolymer, wherein Qis oxygen or sulfur; wherein said prepolymer, upon curing in thepresence of moisture, provides a resililent, crosslinked polymercoating; and

(d) curing said crosslinkable NCQ terminated prepolymer of saidoverlayer to provide an abrasion-resistant crosslinked polymer coatingwhich exhibits an elongation of at least 25%, a tensile strength of atleast 8'00 p.s.i., a tear strength of at least lbs./in., and a peeladhesion to said base layer of at least 5 lbs./ in. width; wherein saidbase layer exhibits higher elongation than said overlayer.

2. The process of claim 1, wherein each said prepolymer comprises thereaction product of at least one polyol and a polyisocyanate.

3. The process of claim 1, wherein each said prepolymer comprises thereaction product of at least one polyether polyol and toluenediisocyanate.

4. The process of claim 1, wherein each said NCQ terminated prepolymeris the reaction product of a toluene diisocyanate and at least onehydroxy terminated polypropylene oxide.

5. The process of claim 1, wherein said surface is concrete.

6. A process in accordance with claim 1, wherein said overlayer isharder than, and is more abrasion-resistant than, said base layer.

7. A process in accordance with claim 6, wherein each said prepolymercomprises the reaction product of at least one polyol and apolyisocyanate.

8. A process in accordance with claim 6, wherein each said prepolymercomprises the reaction product of at least one polyether polyol andtoleune diisocyanate.

9. The process of claim 6, wherein each said NCQ terminated prepolymeris the reaction product of a toluene diisocyanate and at least onehydroxy terminated polypropylene oxide.

10. The process of claim 6, wherein said surface is concrete.

11. The process of claim 6, wherein said surface is asphaltic.

12. The process of claim 6, wherein said surface is wood.

13. The process of claim 6, wherein a polystyrene resin is included insaid base layer in an amount less than 75% by weight of said crosslinkedpolymer.

14. A composite structure comprising:

(a) a trafiic surface,

(b) a base layer firmly bonded to said traffic surface, said base layercomprising a resilient, crosslinked polymer, said polymer being derivedfrom a moisture curable, crosslinkable NCQ terminated prepolymer,wherein Q is oxygen or sulfur; said base layer having an elongation ofat least 200%, a tensile strength of at least 50 p.s.i., and a crackextension characteristic of at least inch at room temperature; and

(c) a tough, hard, wearand abrasion-resistant overlayer bonded to thesurface of said base layer, said tear strength of at least lbs./in.;said overlayer having a peel adhesion to said base layer of at least 5lbs./in. width; wherein said base layer exhibits higher elongation thansaid overlayer. 15. A composite structure in accordance with claim 14,wherein said trafiic surface is concrete.

16. A composite structure in accordance with claim 14, wherein saidtraffic surface is asphalt.

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